Familial Mediterranean fever (FMF) is a rheumatic disease characterized by intermittent bouts of fever with abdominal pain, pleurisy, and/or arthritis; some patients also develop systemic amyloidosis, leading eventually to renal failure. FMF is inherited as a single autosomal recessive gene. The biochemical lesion of FMF, as well as the chromosomal location of the FMF gene, was unknown at the out-set of this project. The purpose of this project has been to identify the FMF gene by the method of positional cloning ("reverse genetics"). During the first two years of this project, we prepared DNA samples from Israeli FMF families and tested for genetic linkage with a panel of polymorphic DNA markers. By this approach, we excluded more than one third of the human genome as the site for the FMF gene. We had also obtained preliminary evidence linking the FMF gene to an area on the long arm of chromosome 17 for some, but not all, families. To clarify the situation, we continued to screen genetic markers. Within the past year we have obtained unequivocal evidence that the FMF gene resides on the short arm of chromosome 16. For a panel of 31 non- Ashkenazi Jewish families, we obtained a maximal pairwise lod score of 22.00, 2 centiMorgans from the PCR marker D16S283. We have identified 8 additional markers in this region of chromosome 16 that confirm linkage. Analyses of linkage heterogeneity ad disease severity in subsets of families indicate that an earlier suggestion of linkage to chromosome 17 was a Type I error. By multipoint linkage analysis and the study of recombinant families, we have identified D16S94 and D16S80 as flanking markers for the FMF gene. Moreover, we have demonstrated linkage disequilibrium between the FMF gene and chromosome 16 markers among Moroccan families. A specific haplotype defined by alleles at D16S291, D16S283, and D16S94, was present in 18/27 Moroccan carrier chromosomes, but 0/27 noncarrier chromosomes. This association was not observed in two other non- Ashkenazi Jewish populations.